The concentration of intracellular free calcium ((Ca2+)i) is a key element in the modulation of a host of cellular processes. Increases in (Ca2+)i during ischemia have been implicated in the mechanisms leading to cell death. 19F and 31P nuclear magnetic resonance (NMR) spectroscopy will be used, in conjunction with fluorinated calcium (5-FBAPTA) and intracellular pH (pHi) indicators (di- and tri-fluoromethyl alanine), to measure (Ca2+)i, high energy phosphates, inorganic phosphate, and pHi in the cat brain in vivo. A ventricular method of perfusion will be developed to administer the membrane-permanent acetoxymethyl esters of each indicator, to determine the optimum loading conditions, and to map the distribution of uptake within the NMR volume by (3H)5-FBAPTA autoradiography. Potential effects of the Ca2+ indicator or cerebral energy metabolism and function will be assessed by the 31P NMR spectrum and electroencephalogram in vivo and by regional ATP measurements in coronal sections. Reversible global ischemia will be produced by intrathoracic clamping of the vessels supplying the brain following the intracerebral loading of the Ca2+ and pHi indicators. The effects of elevated inorganic phosphate and low pHi on (Ca2+)i will be assessed during hypercarbia, a condition where energy failure does not occur. The effects of ATP depletion and high inorganic phosphate, without an accompanying change in pHi, will be assessed during insulin-induced hypoglycemia following electrocerebral silence and in the recovery period after glucose administration. The results of this work will provide new information on the concentration of intracellular Ca2+ in vivo, and how its control is related to the energetic status of the brain. This knowledge should lead to a better understanding of the role of calcium in the etiology of brain damage.